In recent years there has been increasing demand for reliable generation of electricity from renewable energy sources such as wind, solar, tidal or wave sources. Of particular interest is the desire to provide efficient and cost effective electricity generation on a commercial scale. Due to the relative abundance of wave energy, these systems offer the possibility of high levels of efficiency and reliability of supply.
One proposed form of energy converter developed for converting wave energy into electricity consists of a buoy connected to a piston and cylinder arrangement, this converter generally known as a heaving buoy generator. The piston and cylinder arrangement is secured between the buoy and the sea floor, an anchor or reaction plate so that the piston moves linearly within the cylinder in response to movement of the buoy with the waves. The reciprocal action of the piston is used to charge a hydraulic accumulator which is selectively discharged to drive a hydraulic generator. However, the cost of energy (COE) of this type of system remains relatively high. One reason for this is that the wave energy converter is often not in phase, or cannot remain in phase, with the wave resulting in a marked reduction in efficiency of energy capture and corresponding increases in COE.
Reactive control for energy converters, such as the heaving buoy generator described above, offers the potential to vastly increase the efficiency of energy capture and is discussed by Harvard Eidsmoen in “Simulation of a tight moored, amplitude limited heaving buoy wave energy converter with phase control” and “Simulation of a slack moored heaving buoy wave energy converter with phase control”, and the applicant's “Power Take-off Devices—Requirement Setting and Benchmark Review of Existing Technologies, MTSR 3877”, which are incorporated herein in their entirety by way of reference.
However, such technology has not been implemented on commercial scale devices due, it is believed, to the complexity, reliability and efficiency challenges presented by such technologies.